[Rspamd] use boolean for one_shot, fixes #2066

data/conf/rspamd/local.d/metrics.conf

@@ -13,17 +13,17 @@ group "MX" {
 	symbol "MX_INVALID" {
 	  score = 0.5;
 	  description = "No connectable MX";
-	  one_shot = "true";
+	  one_shot = true;
 	}
 	symbol "MX_MISSING" {
 	  score = 2.0;
 	  description = "No MX record";
-	  one_shot = "true";
+	  one_shot = true;
 	}
 	symbol "MX_GOOD" {
 	  score = -0.01;
 	  description = "MX was ok";
-	  one_shot = "true";
+	  one_shot = true;
 	}
 }
 symbol "CTYPE_MIXED_BOGUS" {